feat: add --flavor option to test command

[pdenert]

Summary

Implements feature request #1529 to add a --flavor option to the very_good test command, mirroring Flutter's native flutter test --flavor support.

Status

READY

Description

• Added flavor property (String?) to FlutterTestOptions
• Added --flavor option to TestCommand argParser
• Passes --flavor <value> through to the underlying flutter test command via the arguments list
• Updated tests to verify the option is correctly forwarded

Usage Examples

# Run tests with a specific flavor
very_good test --flavor development

# Combine with other options
very_good test --flavor staging --coverage --min-coverage 100

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore